The team speculates these gamma rays are likely emitted when powerful cosmic rays—produced throughout the universe by violent astrophysical events like supernovae and colliding neutron stars—slam into the sun’s surface.
If a single cosmic ray collides with a particle in the solar atmosphere, it creates a shower of secondary particles and radiation, including gamma rays.
Every 11 years or so its activity crescendos, creating flares and coronal mass ejections—the plasma-spewing eruptions that shower Earth with charged particles and beautiful auroral displays—but then it decrescendos.
Such showers would usually be wholly absorbed by the sun, however.
But according to a hypothesis dating back to the 1990s, some of these secondary showers can be bounced out and away from our star by strong fluctuations in its magnetic field.
Cohen notes these trends might match, but says he cannot currently explain why.
Igor Moskalenko, an astronomer at Stanford University who was not involved in the study, agrees that there is no obvious explanation.